Oil-free air compressor for rail vehicles with air ventilation

ABSTRACT

An oil-free compressor for a rail vehicle includes a multi-piece compressor housing, a first piston cylinder supported in a first opening in the compressor housing, a second piston cylinder supported in a second opening in the compressor housing, a multi-piece crankshaft assembly supported by the compressor housing, and an optionally filtering air plenum in fluid communication with the compressor housing interior to provide a volume of air to the compressor housing interior. The crankshaft assembly is linked to pistons of the first and second piston cylinders by respective connecting rods. The connecting rods connect to a wrist pin associated with each of the pistons, and the wrist pins are respectively supported by a dry lubricant bushing to the associated piston. The compressor housing may have a first housing portion and a second housing portion forming respective halves of the compressor housing.

CROSS REFERENCE TO APPLICATIONS

This application incorporates by reference U.S. patent application Ser.No. 13/350,980, filed Jan. 16, 2012 entitled “Oil-Free Air Compressorfor Rail Vehicles”, which claims the benefit of U.S. Provisional PatentApplication No. 61/437,333, filed Jan. 28, 2011, and entitled “Oil-FeeAir Compressor for Rail Vehicles”, the disclosures of which areincorporated herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to the field of air compressors adapted for useon rail vehicles for the purpose of supplying compressed air topneumatic units associated with the rail vehicle and, in particular, toan oil-free air compressor on a rail vehicle with air ventilation; theoil-free air compressor is used for supplying compressed air to variouspneumatic units associated with the rail vehicle.

2. Description of Related Art

Normally, a pneumatic system is provided for a rail vehicle by which thebrakes of the rail vehicle are operated. An air compressor is used tosupply compressed air to one or more pneumatic units associated with therail vehicle involved in the operation of the brakes. The air compressorusually consists of a driving unit, such as an electric motor, and of acompressor unit, which typically consists of several piston-cylinderarrangements that are driven by a crankshaft. The crankshaft is drivenby the driving unit and includes connecting rods to convert the rotatingmovement of the driving unit into linear movement for each piston tosupply compressed air to the downstream units. Screw-type aircompressors are also generally known in the field for this purpose andare also included within the scope of the present invention.Furthermore, air compressor units for use on rail vehicles may have asingle-stage or a multi-stage construction with at least onelow-pressure stage and one high-pressure stage.

The air compressors used in the rail vehicle field may be subjected tocontinuous operation or to frequent on-and-off operation. In either modeof operation, friction during operation of the compressor leads to highheat development. As a result, in the past, air compressors that werepredominantly used in the rail vehicle field used oil lubrication toensure sufficient cooling during operation. However, oil lubricationcarries a risk that the lubricating oil, usually situated in the housingof the compressor unit in the case of a piston air compressor, canpenetrate past the piston-cylinder interface and into the pneumaticsystem, which may result in oil fouling the pneumatically operated brakeunits on the rail vehicle. Furthermore, condensate, which occurs duringthe required air drying of a pneumatic system, will typically containsome oil that has to be collected for environmental protection reasons.This condensate is typically stored in heatable containers and has to bedrained and disposed of at regular intervals. This collection processleads to increased maintenance and disposal expenditures as well as tohigh oil consumption. In addition to the foregoing difficulties,emulsion formations in the oil circuit of these oil-lubricatedcompressor units can occur if the oil-lubricated compressor units areused infrequently or for limited periods of time as during cold weatheroperation.

Recently, dry-running air compressors have found increased usage in therail vehicle field. A dry-running air compressor operates withoutlubricating oil situated in the housing and is said to be “oil-free”. Inthe case of oil-free air compressors, the lubrication on the pistontravel path is replaced by a particularly low-friction dynamic sealingarrangement. All rotating components are normally disposed in rollerbearings. The encapsulated roller bearings are provided with atemperature-stable long-lived grease filling. In the valve area,slidably guided components are largely avoided. Because of thesemeasures, oil lubrication is not required in the air compressor unit.The risk of fouling by oil of the compressed air can therefore also beexcluded. As a result of the elimination of an oil circuit, the oil-freeair compressor can have a relatively light construction. In the railvehicle field, there is a current trend toward lighter construction, andlight carrier structures are also increasingly used for frameconstructions. However, such light carrier structures frequently have anumber of unfavorable natural frequencies that are close to therotational speed of the air compressor of the pneumatic system which isarranged thereon. Therefore, it is difficult to sufficiently observe therequired specifications concerning permissible structure-born noiselevels.

U.S. Pat. No. 6,776,587 to Hartl et al. and U.S. Pat. No. 7,059,841 toMeyer et al. are patents directed to oil-free air compressor technology.The Meyer et al. patent discloses an arrangement of an oil-freecompressor apparatus on a rail vehicle for supplying compressed air topneumatic units assigned to the rail vehicle. The arrangement includesan oil-free air compressor and a cooler unit connected with the aircompressor. The arrangement also includes a rail vehicle having a floorwith at least one opening. The air compressor is fastened on at leastone side to the vehicle floor such that a main axis of rotation of theair compressor is arranged essentially vertical with respect to thevehicle floor. The Hartl et al. patent discloses a piston arrangementfor a dual-stage piston air compressor that includes a crankshaft andseveral piston-cylinders. The arrangement allows two or morelow-pressure stages and at least one high-pressure stage to be formed.The arrangement allows the two or more low-pressure cylinders to bearranged in relation to the high-pressure stage in such a way that saidtwo or more low-pressure cylinders are in phase or are offset by lessthan a predetermined amount and compress in a position which is offsetby another predetermined amount in relation to one or more of thehigh-pressure cylinders.

United States Patent Application Publication No. 2007/0292289 to Hartlet al. discloses a compressor piston including a piston and a cylinder,a connecting rod connecting the piston to a crankshaft in a crankcase bya roller bearing, an air inlet line, and an air outlet line in acylinder head. A tube connection between the air inlet line and thecrankcase transports cooling air from the inlet line to the crankcase.The tube connection is exterior of the cylinder. An air inlet valve isconnected to the tube connection which opens when the pressure in thecrankcase is less than the pressure in the air inlet line, and an airoutlet valve is connected to the crankcase which opens when the pressurein the crankcase exceeds a predetermined value.

Further, United States Patent Application Publication No. 2009/0016908to Hartl et al. discloses a multi-cylinder dry-running piston compressorfor generating compressed air. The piston compressor includes acrankcase having an interior and a crankshaft rotatably mounted in thecrankcase. Also included are two connecting rods mounted on thecrankshaft and configured to run counter to one another. Furtherincluded are two cylinders mounted in the crankcase and a pistonarranged at an end of each of the connecting rods and configured to runin a respective one of the two cylinders.

SUMMARY OF THE INVENTION

In one embodiment, an oil-free compressor for a rail vehicle includes acompressor housing comprising at least a first housing portion and asecond housing portion, a first piston cylinder supported in a firstopening in the compressor housing, a second piston cylinder supported ina second opening in the compressor housing and fluidly connected to thefirst piston cylinder, a multi-piece crankshaft assembly supported bythe compressor housing and linked to the pistons of the first and secondpiston cylinders by respective connecting rods, and an air plenum influid communication with the compressor housing interior to provide avolume of air to the compressor housing interior.

The first housing portion and the second housing portion may formrespective halves of the compressor housing and may be secured togetherwith mechanical fasteners. The first piston cylinder may be larger thanthe second piston cylinder. The crankshaft assembly may comprise acrankshaft center section and two end sections. The end sections maycontain counterweights. Opposing ends of the crankshaft center sectionmay be secured within respective cavities in the end sections. Thecrankshaft center section may comprise a first arm section offset from asecond arm section and each of the arm sections may define acircumferential recess for receiving a bearing associated with therespective connecting rods. The end sections may be mounted to thecrankshaft center section to secure the bearings associated with therespective connecting rods.

The oil-free compressor may include having the air plenum in fluidcommunication with the first piston cylinder. The oil-free compressormay further comprise an air intake valve, such as a check valve or reedvalve, in the compressor housing enabling air to be drawn into thecompressor housing interior from the air plenum. Moreover, the oil-freecompressor may further comprise an air discharge valve, such as a checkvalve or reed valve, in the compressor housing enabling air to bedischarged from the compressor housing interior.

In another embodiment, the oil-free compressor for a rail vehicleincludes a multi-piece compressor housing, a first piston cylindersupported in a first opening in the compressor housing, a second pistoncylinder supported in a second opening in the compressor housing andfluidly connected to the first piston cylinder, and a multi-piececrankshaft assembly supported by the compressor housing and linked tothe pistons of the first and second piston cylinders by respectiveconnecting rods. The connecting rods may connect to a wrist pinassociated with each of the pistons, and the wrist pins are respectivelysupported by a dry lubricant bushing to the associated piston. Theoil-free compressor may further comprise an air plenum in fluidcommunication with the compressor housing interior to provide a volumeof air to the compressor housing interior.

The compressor housing may comprise at least a first housing portion anda second housing portion. The first housing portion and the secondhousing portion may form respective halves of the compressor housing andmay be secured together with mechanical fasteners. The first pistoncylinder may be larger than the second piston cylinder. The crankshaftassembly may comprise a crankshaft center section and two end sections.The end sections may contain counterweights. Opposing ends of thecrankshaft center section may be secured within respective cavities inthe end sections. The crankshaft center section may comprise a first armsection offset from a second arm section and each of the arm sectionsmay define a circumferential recess for receiving a bearing associatedwith the respective connecting rods. The end sections may be mounted tothe crankshaft center section to secure the bearing associated with therespective connecting rods. The dry lubricant bushing may be coated withPEAK or comprise a PEAK liner.

The oil-free compressor may include having the air plenum in fluidcommunication with the first piston cylinder. The oil-free compressormay further comprise an air intake valve, such as a check valve or reedvalve, in the compressor housing enabling air to be drawn into thecompressor housing interior from the air plenum. Moreover, the oil-freecompressor may further comprise an air discharge valve, such as a checkvalve or reed valve, in the compressor housing enabling air to bedischarged from the compressor housing interior.

Further details and advantages will become apparent upon reviewing thedetailed description set forth herein in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an oil-free air compressor for railwayvehicles shown in association with a drive motor and cooling fan.

FIG. 2 is a first perspective and isolation view of the oil-free aircompressor shown in FIG. 1.

FIG. 3 is a second perspective and isolation view of the oil-free aircompressor shown in FIG. 1.

FIG. 4 is a third perspective and isolation view of the oil-free aircompressor shown in FIG. 1.

FIG. 5 is a cross-sectional view taken along lines 5-5 in FIG. 4.

FIG. 6 is a longitudinal cross-sectional view of the oil-free aircompressor shown in FIG. 1.

FIG. 7 is an exploded perspective and isolation view of a piston of theoil-free air compressor shown in FIG. 1.

FIG. 8 is a cross-sectional view of an assembled piston of the oil-freeair compressor shown in FIG. 1.

FIG. 9 is an exploded perspective view of a multi-component compressorhousing of the oil-free air compressor shown in FIG. 1.

FIG. 10 is a perspective view of a multi-component crankshaft assemblyof the oil-free air compressor shown in FIG. 1.

FIG. 11 is a longitudinal cross-sectional view of the multi-componentcrankshaft assembly of FIG. 10.

FIG. 12 is an exploded perspective view of another embodiment of themulti-component crankshaft assembly for a three-cylinder embodiment ofthe oil-free air compressor shown in FIG. 1.

FIG. 13 is a cross-sectional view of the multi-component crankshaftaccording to another embodiment.

FIG. 14 is a perspective view of an embodiment of an oil-free aircompressor for railway vehicles with air ventilation.

FIG. 15 is a cross-section view taken along lines 15-15 in FIG. 14.

FIG. 16 is a bottom view of a portion of the housing of the oil-free aircompressor shown in FIGS. 14-15.

DESCRIPTION OF THE INVENTION

For purposes of the description hereinafter, spatial orientation terms,as used, shall relate to the referenced embodiment as it is oriented inthe accompanying drawing figures or otherwise described in the followingdetailed description. However, it is to be understood that theembodiments described hereinafter may assume many alternative variationsand configurations. It is also to be understood that the specificcomponents, devices, and features illustrated in the accompanyingdrawing figures and described herein are simply exemplary and should notbe considered as limiting.

Referring to FIGS. 1-6, an air compressor 2 according to one embodimentis shown. As shown, the air compressor 2 is a multi-cylinder aircompressor 2 comprising at least a first piston-cylinder 10 and a secondpiston-cylinder 100. The respective first and second piston-cylinders10, 100 (hereinafter referred to as “first piston cylinder 10” and“second piston cylinder 100”) are supported by a compressor housing orcrankcase 170 and are each driven by a crankshaft assembly 240 disposedwithin the compressor housing 170 and rotationally supported by thecompressor housing 170. The foregoing components of the air compressor 2are described in detail herein.

As shown in cross-section in FIG. 5, the first and second pistoncylinders 10, 100 are of substantially identical construction with thefirst piston cylinder 10 operating as the first cylinder and the secondpiston cylinder 100 operating as the second cylinder in themulti-cylinder air compressor 2. The first piston cylinder 10 isgenerally larger than the second piston cylinder 100 and has an overalllarger diameter than the second piston cylinder 100. The first pistoncylinder 10 comprises a cylindrical housing 12 that has a first end 14adapted to be inserted into a corresponding opening, as describedherein, in the compressor housing 170, and a second end 16. Thecylindrical housing 12 is formed with a flange 18 located proximal ofthe first end 14 for interfacing with the exterior of the compressorhousing 170. Heat-dissipating fins 19 may be provided about thecylindrical housing 12, and the cylindrical housing 12 may be formed ofany suitable material providing sufficient strength and heat-dissipatingcharacteristics such as aluminum.

A cylinder head 20 is secured to the second end 16 of the cylindricalhousing 12. The cylinder head 20 generally comprises a valve plate 22and an air connecting unit 24, with the air connecting unit 24 securingthe valve plate 22 on the second end 16 of the cylindrical housing 12via mechanical fasteners 26. An additional mechanical fastener 27secures the valve plate 22 to the air connecting unit 24. The airconnecting unit 24 comprises an air inlet port 28. An air intake line 30extends from the air inlet port 28 and is connected to the compressorhousing 170 as described herein. The air connecting unit 24 furthercomprises an air outlet port 32. An air connecting line 34 extends fromthe air outlet port 32 to fluidly couple, either directly or indirectly,to an air inlet port provided on the second piston cylinder 100 asdescribed herein. Additionally, the valve plate 22 comprises aconventional reed valve assembly (not shown) for permitting airflow intothe cylindrical housing 12 via the air intake line 30 and the air inletport 28 and to be expelled from the cylindrical housing 12 via the airoutlet port 32 and the air connecting line 34, to provide pressurizedair to the second piston cylinder 100. The air connecting unit 24, theair intake line 30, and the air connecting line 34 may be formed of anysuitable material providing sufficient strength and heat transfercharacteristics such as aluminum. The cylindrical housing 12 defines aninterior surface 36.

Referring additionally to FIGS. 7-8, the first piston cylinder 10further comprises a piston 40 that is reciprocally operable within thecylindrical housing 12. The piston 40 comprises a first end 42 and asecond end 44, and is made of any suitable material providing sufficientstrength and heat transfer characteristics such as aluminum. One or morewear bands or rings 46 is provided about the body of the piston 40proximal of the first end 42 of the piston 40. The wear bands or rings46 are desirably non-metallic to interface with the interior surface 36of the cylindrical housing 12 and may be made of a Torlon®polyamide-imide. A pair of piston rings 48 is provided about the firstend 42 of the piston 40 and which also interfaces with the interiorsurface 36 of the cylindrical housing 12. The piston rings 48 aredesirably also of non-metallic construction, such as Teflon® (e.g.,PTFE), to form a generally fluid-tight seal with the interior surface 36of the cylindrical housing 12. The body of the piston 40 defines anaxial cavity or recess 50 and a transverse cavity or bore 52, which isgenerally orthogonal to the axial cavity or recess 50. The transversebore 52 supports a wrist pin 54 that extends transversely through thebody of the piston 40. The wrist pin 54 may be a solid wrist pin or, asillustrated, a cylindrical-shaped wrist pin 54. The wrist pin 54 is heldin place within the transverse bore 52 by mechanical fasteners 55 thatextend into second end 44 of the piston 40 to engage the wrist pin 54.The wrist pin 54 is provided to interface or link with a connecting rodassociated with the crankshaft assembly 240, as described furtherherein. The wrist pin 54 may be made of any suitable material providingsufficient strength and heat transfer characteristics such as aluminum.

Known wrist pin assemblies are generally solid shaft wrist pins where aneedle bearing is fitted. These wrist pins are precision-ground and actas an inner race for the needle bearing. These wrist pins must have across-sectional area large enough to withstand bending stresses at theircenters, and their surfaces must be hard enough to withstand the loadingof the needle rollers of the bearing. The needle bearing requires hightemperature grease and high temperature seals to contain the grease in abearing cavity. These prior art wrist pins can slide within the needlebearing and, therefore, the ends of the wrist pins must be fastened tothe piston with fasteners, and shock absorbing non-metallic bushingsthat are located between the wrist pin ends and the piston wrist pinbore.

The wrist pin 54, described previously, is supported in the transversebore 52 by an oil-free assembly that is comprised by a pair of drylubricant bushings 56 that are press-fitted into the transverse bore 52.The dry lubricant bushings 56 typically comprise a metal case with apolymer liner. Dry bushings are usually plain composite bushes that areable to run with marginal or no lubrication and have a low coefficientof friction. Dry bushings can include polymer dry bushings and alloybushings. This oil-free assembly allows the transmission of compressionand suction forces from a center portion 58 of the wrist pin 54 to theopposing ends 60, 62 of the wrist pin 54, thus reducing the bendingmoment of the wrist pin 54 and allowing the wrist pin 54 to have auniform cross-section of homogeneous material with no additionalcomponents thereby reducing weight. The dry lubricant bushings 56 alsoprovide bearing support transmitted directly through the piston 40instead of the load being transmitted directly through the connectingrod associated with the crankshaft assembly 240, as described furtherherein. Consequently, the load due to compression is supported bygreater bearing area and greater bearing capacity. In addition, the drylubricant bushings 56 self-lubricate as the dry lubricant bushings 56are coated with PEAK material or comprise a PEAK liner. In operation,the self-lubricating, dry lubricant bushings 56 lubricate the slidingjoint made between the dry lubricant bushings 56 and the wrist pin 54.The dry lubricant bushings 56 and the wrist pin 54 described previouslyeliminate the need for a “thick” wrist pin as required in the prior artbecause compression loading shifts from the center portion 58 of thewrist pin 54 to the two ends 60, 62 of the wrist pin 54. Since the wristpin 54 does not have to withstand bending stresses at its center portion58, the surface of the wrist pin 54 need not be hard enough to withstandthe loading of a needle bearing, as described herein in connection withthe crankshaft assembly 240. Additionally, there is no requirement forhigh temperature grease and high temperature seals to contain the greasein a bearing cavity. Further, the wrist pin cannot slide within theneedle bearing since the wrist pin 54 is press-fitted in the hoop of theconnecting rod. Therefore, the ends 60, 62 of the wrist pin 54 can befree to float without any fasteners. The shock absorbing non-metallicbushings required in the prior art wrist pins discussed previously arealso eliminated. These characteristics are also present in the wrist pindiscussed herein in connection with the second piston cylinder 100.

In operation, the piston 40 operates in a reciprocating movement whichis generated via the crankshaft assembly 240. Air within the compressorhousing 170 is drawn into the cylinder housing 12 via the air intakeline 30 and the air inlet port 28 as a result of the downward movementof the piston 40 and is compressed during the upward movement of thepiston 40. The reed valve associated with the valve plate 22 has aportion that is opened during the downward movement of the piston 40,drawing air into the cylinder housing 12 from the air intake line 30 andthe air inlet port 28, and closes during the upward movement. Further,the reed valve (not shown) has another portion that closes during thedownward movement of the piston 40 and opens in the upward movement ofthe piston 40 whereby the air in the cylinder housing 12 is compressedand is guided out of the cylinder housing 12 via the air outlet port 32and the air connecting line 34 and is fed to the air inlet port,discussed herein, associated with the second piston cylinder 100.

As noted previously, the second piston cylinder 100 has substantiallyidentical construction to the first piston cylinder 10, as now describedhereinafter. The first piston cylinder 10 is generally larger than thesecond piston cylinder 100 and has an overall larger diameter than thesecond piston cylinder 100. The second piston cylinder 100 comprises acylindrical housing 112 that has a first end 114 adapted to be insertedinto a corresponding opening, as described herein, in the compressorhousing 170, and a second end 116. The cylindrical housing 112 is formedwith a flange 118 located proximal of the first end 114 for interfacingwith the exterior of the compressor housing 170. Heat-dissipating fins119 may be provided about the cylindrical housing 112, and thecylindrical housing 112 may be formed of any suitable material providingsufficient strength and heat-dissipating characteristics such asaluminum.

A cylinder head 120 is secured to the second end 116 of the cylindricalhousing 112. The cylinder head 120 generally comprises a valve plate 122and an air connecting unit 124, with the air connecting unit 124securing the valve plate 122 on the second end 116 of the cylindricalhousing 112 via mechanical fasteners 126. An additional mechanicalfastener 127 secures the valve plate 122 to the air connecting unit 124.The air connecting unit 124 comprises an air inlet port 128 which isfluidly connected (directly or indirectly) to the air connecting line 34that extends from the air outlet port 32 associated with the airconnecting unit 24 of the first piston cylinder 10. As shown in FIG. 1,an air manifold 300 may be provided as an intermediary device in the airconnecting line 34 that extends from the air outlet port 32 associatedwith the air connecting unit 24 of the first piston cylinder 10 to theair inlet port 128 on the air connecting unit of the second pistoncylinder 100. The air connecting unit 124 further comprises an airoutlet port 132 which is connected via an air connecting line 134 to adownstream requirement or apparatus, such as an outlet air manifold 302.Additionally, the valve plate 122 comprises a conventional reed valveassembly (not shown) for permitting airflow into the cylindrical housing112 via the air connecting line 34 and the air inlet port 128 and to beexpelled from the cylindrical housing 112 via the air outlet port 132and the air connecting line 134, to provide pressurized air via the airconnecting line 134 to a downstream requirement, such as the outlet airmanifold 302. The air connecting unit 124 and the air connecting line134 may be formed of any suitable material providing sufficient strengthand heat transfer characteristics such as aluminum. The cylindricalhousing 112 defines an interior surface 136.

With continued reference to FIGS. 1-8, the second piston cylinder 100also comprises a piston 140 that is reciprocally operable within thecylindrical housing 112. The piston 140 comprises a first end 142 and asecond end 144. One or more wear bands or rings 146 are provided aboutthe body of the piston 140 proximal of the first end 142 of the piston140. The wear bands or rings 146 are desirably non-metallic to interfacewith the interior surface 136 of the cylindrical housing 112, and may bemade of a Torlon® polyamide-imide. A pair of piston rings 148 isprovided about the first end 142 of the piston 140 and which alsointerfaces with the interior surface 136 of the cylindrical housing 112.The piston rings 148 are desirably of non-metallic construction, such asTeflon® (e.g., PTFE), to form a generally fluid-tight seal with theinterior surface 136 of the cylindrical housing 112. The body of thepiston 140 defines an axial cavity or recess 150 and a transverse cavityor bore 152, which is generally orthogonal to the axial cavity or recess150. The transverse bore 152 supports a wrist pin 154 that extendstransversely through the body of the piston 140. The wrist pin 154 maybe a solid wrist pin or, as illustrated, a cylindrical-shaped wrist pin154. The wrist pin 154 is held in place within the transverse bore 152by mechanical fasteners 155 that extend into second end 144 of thepiston 140 to engage the wrist pin 154. The wrist pin 154 is provided tointerface or link with a connecting rod associated with the crankshaftassembly 240, as described further herein. The wrist pin 154 may be madeof any suitable material providing sufficient strength and heat transfercharacteristics such as aluminum.

In a similar manner to the wrist pin 54, the wrist pin 154 is alsosupported within the transverse bore 152 by an oil-free assembly that iscomprised of a pair of dry lubricant bushings 156 which are press-fittedin the transverse bore 152. The dry lubricant bushings 156 typicallycomprise a metal case with polymer liner. This oil-free assembly allowsthe transmission of compression and suction forces from a center portion158 of the wrist pin 154 to the ends 160, 162 of the wrist pin 154 thusreducing the bending moment of the wrist pin 154 and allowing the wristpin 154 to have a uniform cross-section of homogeneous material with noadditional components thereby reducing weight. The dry lubricantbushings 156 also provide bearing support transmitted directly throughthe piston 140 instead of the load being transmitted directly throughthe connecting rod. Consequently, the load, due to compression, issupported by greater bearing area and greater bearing capacity. Inaddition, the dry lubricant bushings 156 self-lubricate as the drylubricant bushings 156 are coated with PEAK material or include a PEAKliner. In operation, the self-lubricating, dry lubricant bushings 156lubricate the sliding joint made between the dry lubricant bushings 156and the wrist pin 154. The various advantages described previously withrespect to the wrist pin 54 are likewise applicable to the wrist pin154.

In operation, the piston 140 operates in a reciprocating movement whichis generated via the crankshaft assembly 240. Air is drawn into thecylinder housing 112 via the air connecting line 130 and the air inletport 128 as a result of the downward movement of the piston 140 and iscompressed during the upward movement of the piston 140. The reed valveassembly (not shown) associated with the valve plate 122 has a portionthat is opened during the downward movement of the piston 140, drawingair into the cylinder housing 112 from the air connecting line 130 andthe air inlet port 128 and closes during the upward movement. Further,the reed valve (not shown) includes another portion that is closedduring the downward movement of the piston 140 and opens in the upwardmovement of the piston 140 whereby the air in the cylinder housing 112is compressed and is guided out of the cylinder housing 112 via the airconnecting line 134 and is fed via the air connecting line 134 to adownstream requirement such as the outlet air manifold 302.

Referring additionally to FIG. 9, the compressor housing or crankcase170 is desirably a compound structure comprising at least a firsthousing portion 172 and a second housing portion 174. The first andsecond housing portions 172, 174 are each generally rectangular shapedstructures that are adapted to be joined together to form the overallcompressor housing 170. For this purpose, the first and second housingportions 172, 174 have respective lateral flanges 176, 178 that areadapted to be joined together using conventional mechanical fasteners177, such as bolt and nut combinations. Locating bushings 179 may beprovided on the lateral flanges 176, 178 to properly align correspondingopenings in the lateral flanges 176, 178 to accept the mechanicalfasteners 177. The first housing portion 172 defines an opening 180sized to accept the first end 14 of the cylindrical housing 12 of thefirst piston cylinder 10. Similarly, the second housing portion 174defines an opening 182 sized to accept the first end 114 of thecylindrical housing 112 of the second piston cylinder 100. Mountingelements 184 may be welded or otherwise secured at locations about therespective openings 180, 182. The mounting elements 184 may be mountingpegs or bolts that are adapted to engage openings (not shown) in therespective flanges 18, 118 on the cylindrical housings 12, 112 of thefirst and second piston cylinders 10, 100 to secure the piston cylinders10, 100 in place within the openings 180, 182 with conventional nuts orlike fastening components.

As shown in FIG. 4, the first housing portion 172 further comprisesopposing lateral walls 186. The air intake line 30 is placed in fluidcommunication with an air intake port or opening 188 and may be definedin the first housing portion 172 in one of the opposing lateral walls186 and is secured via mechanical fasteners to the lateral wall 186 ofthe first housing portion 172 to place the first piston cylinder 10 influid communication with the interior of the compressor housing 170. Asan alternative, the air intake port or opening 188 may be provided inthe same wall of the first housing portion 170 supporting the firstpiston cylinder 10 and this modification is also shown in FIGS. 2-3 andin cross-section in FIG. 6. FIG. 9 shows both locations for air intakeport 188, and when not in use, the unused air intake port 188 is coveredby a cover plate 189. The second housing portion 174 further includes anair intake port 190 for providing air intake generally to the interiorof the assembled compressor housing 170. The air intake port 190 may beadapted to interface or connect to an air inlet line 192 connected to afiltering apparatus 304 for filtering air entering the compressorhousing 170, as shown in FIG. 1.

The first housing portion 172 and second housing portion 174, whenassembled as described previously, form the compressor housing 170. Whenthe first piston cylinder 10 and second piston cylinder 100 are securedin the respective openings 180, 182 in the first housing portion 172 andsecond housing portion 174, the respective first and second pistoncylinders 10, 100 extend outward from opposing longitudinal walls 194 ofthe compressor housing 170. Two end walls 196 of the compressor housing170 are defined by assembly of the first and second housing portions172, 174 and these end walls 196 define respective axial openings 198,200 in the compressor housing 170.

In summary, the compressor housing 170 as depicted is made up of atleast two separate “halves” in the form of housing portions 172, 174that are assembled together and machined as one. The two halves arelocated with respect to each other by the locating bushings 179 and heldtogether by mechanical fasteners 177. Benefits of the split compressorhousing 170 relate to manufacturing and assembly costs, for example.Because the compressor housing 170 is in at least two major parts, thetooling required to cast the compressor housing 170 may be smaller and,as a result, more foundries are capable of manufacturing this component.This manufacturing advantage can lead to cost savings over a largeone-piece housing that requires large tooling and equipment to cast. Asknown in the art, a one-piece compressor crankcase must be large becausethe crankshaft has to be assembled before it is placed into thecrankcase, and an opening must be provided in the crankcase that islarge enough to allow the assembled crankshaft to pass therethrough.Installing an assembled crankshaft through an opening in a one-piececrankcase that is just large enough to accommodate the crankshaft istime consuming and difficult. Typically, the crankshaft has to becarefully threaded into the crankcase while continually repositioningthe connecting rods to avoid contact with the inside of the crankcase. Asingle piece crankshaft can weigh over 80 pounds and maneuvering it isvery difficult. The presently disclosed compressor housing 170 allowsthe crankshaft assembly 240 to be assembled and held stationary whilethe at least two housing portions 172, 174 are placed on either side ofthe crankshaft assembly 240 and secured. This assembly step eliminatesthe need to manipulate a heavy crankshaft as in the prior art. Byproviding a compound compressor housing 170, overall, the compressorhousing 170 may be made smaller, lighter, easier to cast and machine,and easier to assemble. The first and second housing portions 172, 174forming the compressor housing 170 may be formed of any suitablematerial providing sufficient strength and heat-dissipatingcharacteristics such as aluminum.

The first axial opening 198 in the compressor housing 170 supports afirst crankshaft mounting element 202, which generally encloses thefirst axial opening 198 and is supported to the end wall 196 of thecompressor housing 170 via mechanical fasteners 203. The firstcrankshaft mounting element 202 comprises an annular portion 204 that isseated within a receiving annular portion 206 formed by the assembly ofthe first housing portion 172 and second housing portion 174. Theannular portion 204 of the first crankshaft mounting element 202supports a first main crankshaft bearing 208 which, in turn, supportsone end of the crankshaft assembly 240. The first main crankshaftbearing 208 is sealed in place by a first shaft seal 210 adapted to seatagainst the crankshaft assembly 240, and a second shaft seal 212disposed interiorly within the annular portion 204 of the firstcrankshaft mounting element 202. The first crankshaft mounting element202 also supports an external mounting cage 214 for mounting the aircompressor 2 in association with a drive component such as a drive motor306.

The second axial opening 200 in the compressor housing 170 supports asecond crankshaft mounting element 222, which generally encloses thesecond axial opening 200 and is supported to the opposing end wall 196of the compressor housing 170 via mechanical fasteners 223. The secondcrankshaft mounting element 222 comprises an annular portion 224 that isseated within a receiving annular portion 226 defined by the assembly ofthe first housing portion 172 and second housing portion 174. Theannular portion 224 of the second crankshaft mounting element 222supports a second main crankshaft bearing 228 which, in turn, supportsthe other end of the crankshaft assembly 240. The second main crankshaftbearing 228 is sealed in place by a first shaft seal 230 adapted to seatagainst the crankshaft assembly 240, and a second shaft seal 232disposed interiorly within the annular portion 224 of the secondcrankshaft mounting element 222. The respective first and secondcrankshaft mounting elements 202, 222 support the opposing ends of thecrankshaft assembly 240 and enclose the first and second axial openings198, 200 defined by the assembly of the first and second housingportions 172, 174 which form the compressor housing 170. As shown inFIGS. 1-4 and 9, the first and second housing portions 172, 174 defineseveral additional openings 234 to provide access to the interior of thecompressor housing 170 or to provide other points of connection foradditional air handling conduits to the compressor housing 170. Theseadditional openings 234 may be covered with additional covers 236 thatare secured to the compressor housing 170 via appropriate mechanicalfasteners.

Referring additionally to FIGS. 10-12, the crankshaft assembly 240 is acompound assembly comprised generally by a crankshaft center section 242and two crankshaft end sections 244, 246. The first crankshaft endsection 244 is supported by the first main crankshaft bearing 208 in thefirst crankshaft mounting element 202. As described previously, thefirst crankshaft mounting element 202 supports the external mountingcage 214 for mounting the air compressor 2 in association with a drivecomponent such as the drive motor 306 shown in FIG. 1. Thus, the firstcrankshaft end section 244 is positioned to interface with a drive motorto impart rotary motion to the crankshaft assembly 240. The oppositecrankshaft end section 246 is supported by the second main crankshaftbearing 228 in the second crankshaft mounting element 222 and this endsection 246 is positioned to interface with a cooling air fan 308associated with the air compressor 2. Opposing ends 248 of thecrankshaft center section 242 are secured within respective cavities 250in the crankshaft end sections 244, 246 by a press-fit connection andlike connections.

As shown in FIGS. 10-11, the crankshaft assembly 240 includes at leasttwo connecting rods 252, 254 which link to the pistons 40, 140,respectively, of the first and second piston cylinders 10, 100. Theconnecting rods 252, 254 each comprise a first circular end flange 256supported on the crankshaft center section 242 by respective sphericalroller bearings 258 that are press-fit into respective circumferentialrecesses 260 defined adjacent the respective ends 248 of the crankshaftcenter section 242. The spherical roller bearings 258 are held in placein the recesses 260 by the respective press-fit crankshaft end sections244, 246. Referring briefly to FIG. 12, while the foregoing discussionrelates to an air compressor 2 having two compressing piston-cylindersprovided by the first and second piston cylinders 10, 100, additionalpiston-cylinders may be included in the air compressor 2. FIG. 12 showsthat if one or more additional piston cylinders (not shown) are added tothe air compressor 2, an additional connecting rod 262 may be mounted onthe crankshaft center section 242 adjacent the connecting rod 254 toprovide motive forces for operating the additional piston cylinder (notshown). Spacers 264 of predetermined lengths may also be used to mountthe respective connecting rods 252, 254, 262 to the crankshaft centersection 242 as needed in this embodiment.

The connecting rods 252, 254 each comprise a second circular end flange266 supported on the respective wrist pins 54, 154 associated with thepistons 40, 140 by respective needle bearings 268. Shaft seals 270 areprovided outboard on either side of each of the spherical rollerbearings 258 and about the crankshaft center section 242 to seal thespherical roller bearings 258. Likewise, shaft seals 272 are providedoutboard on either side of each of the needle bearings 268 and about therespective wrist pins 54, 154 to seal the needle bearings 268. Further,as shown in cross-section in FIG. 11, the crankshaft center section 242generally comprises an offset construction defined by two opposed shaftportions or arm sections 274, 276 that terminate in ends 248. Respectiveinternal passages 278, 280 are defined in the shaft arm sections 274,276 that are each sealed with a plug 282. The crankshaft center section242, end sections 244, 246, and connecting rods 252, 254, 262 may beformed of any suitable material providing sufficient strength such assteel.

The multi-piece crankshaft assembly 240 may be used to replace one-piececrankshafts which are large and heavy. Such single-piece crankshafts arecast or forged by large machinery that requires expensive tooling.Additionally, special machines are needed to machine and balance aone-piece crankshaft. With a one-piece crankshaft, the bearings for theconnecting rods have to be sized so that they can be installed on theone-piece crankshaft, often over the bearing seat for the crankshaftmain bearings. This means the bearings for the connecting rods have tobe larger than necessary, thus adding more weight and bulk. Also, thisprior art arrangement requires the addition of bolt-on counterweightswhich could become loose and cause compressor failure.

The multi-piece crankshaft assembly 240 described hereinabove is made upof a crankshaft center section 242 that is relatively small and can bemade from a casting or forging. The two crankshaft end sections 244, 246also contain counterweights as integral parts and require no fasteners.The foregoing components are small enough to be cast or forged withoutlarge equipment. Thus, specialized crankshaft manufacturing equipment isalso unnecessary. Since the spherical roller bearings 258 associatedwith the connecting rods 252, 254, 262 do not have to pass overcrankshaft main bearing seats or over crankshaft bends as in a one-piececrankshaft situation, they can be sized based on the loading of thepistons 40, 140 and, as a result, may be smaller.

The crankshaft center section 242 may be designed with the proper throwbased on the intended application, including a motor end shaft armsection 274 with the same throw and appropriate end counterweightsection 244 and a fan end shaft arm section 276 with the same throw andappropriate end counterweight section 246. The spacers 264 are also usedto hold the spherical roller bearings 258 and place them in the properlocation in a multi-connecting rod arrangement as shown in FIG. 12. Thecrankshaft center section 242 is provided to hold the connecting rods252, 254, 262 by securing the spherical roller bearings 258 in theproper location. As noted previously, for air compressors 2 of more thantwo piston cylinders, the spacers 264 hold the associated sphericalroller bearings 258 in place by pressing onto the inner bearing race foreach bearing 258. The crankshaft center section 242 is also provided sothat the opposing ends 248 are press-fit into the respective cavities250 in the crankshaft end sections 244, 246. The two crankshaft endsections 244, 246 contain the crankshaft center section 242 and pressonto the inner race of the spherical roller bearings 258, or onto thespacers 264 which press onto the inner races of the spherical rollerbearings 258 in a multi-connecting rod arrangement as shown in FIG. 12.The interface between the spherical roller bearings 258 and thecrankshaft center section 242 does not have to be a press-fit interfacebecause the crankshaft end sections 244, 246 or the spacers 264 aresufficient to hold the inner races from spinning To enable easydisassembly of the crankshaft assembly 240 for replacing the connectingrod bearings 268 at overhaul, holes may be drilled into the crankshaftcenter section 242 to intersect with internal passages 278, 280 and aredefined in the shaft arm sections 274, 276 so that a hydraulic pump maybe attached to push-off the two crankshaft end sections 244, 246 fromthe center section 242.

Moreover, as shown in FIG. 13, in another embodiment the crankshaftcenter section 242 comprises an offset construction defined by twoopposed and separate shaft portions or aim sections 274, 276 thatterminate in ends 248. Respective internal passages 278, 280, which arenot shown FIG. 13 but may be in the form shown in FIG. 11 discussedpreviously, may be defined in the shaft aim sections 274, 276 and besealed with respective plugs 282. The crankshaft center section 242 inFIG. 13 defines a pair of through holes 292 to accept mating ends 298 ofthe respective shaft portions or arm sections 274, 276. Themulti-component crankshaft center section 242 may be readily be used inplace of the singular or unitary crankshaft center section 242 discussedpreviously. The multi-component crankshaft center section 242facilitates easier manufacturing. The mating ends 298 may be secured inthe through holes 292 via mechanical fastening or friction fit methodsand like methods known in the mechanical arts.

Referring to FIGS. 14-16, another embodiment of the air compressor 2 isshown. The air compressor 2 shown in FIGS. 14-16 is adapted to improvethe exchange of air in the compressor housing or crankcase 170, whichaids in extending the longevity of the air compressor 2. In theembodiments of the air compressor 2 described previously, cooling airflows are drawn into the crankcase 170 due to the suction strokes of thepistons 40, 140 (see FIG. 6) in the first piston cylinder 10. Thismethod is effective at cooling the crankcase 170 but may have the effectof lowering the overall efficiency of the air compressor 2 due to theintroduction of preheated suction air into the first piston cylinder 10.In the modified embodiment shown in FIGS. 14-16, an arrangement andmethod is provided that brings cool air into the crankcase 170 anddischarges heated air therefrom while having minimal effect on aircompressor efficiency.

As shown in FIGS. 14-16, an air plenum 400 is disposed on the crankcase170, typically on the second housing portion 174 thereof. The air plenum400 generally rectangular shaped (e.g., box-shaped) housing 402 thatdefines a hollow interior 404, which provides a volume of air that canbe drawn into crankcase 170. An end wall 406 of the housing 402 definesan air inlet 408 which may be connected to an air filter or otherapparatus (not shown) used to filter cool ambient air entering the airplenum housing 402 via the inlet 408 and thereby providing a volume offiltered air in the air plenum housing 402. Other advantages of the airplenum 400 are that the air plenum 400 serves to depulse the intake airprior to entering the first piston cylinder 10 aiding in the inductionof air and dampening the intake noise of the air compressor 2contributing to overall noise reduction. The air plenum housing 402 isconnected to the first piston cylinder 10 via the air intake line 30. Asidewall 410 of the air plenum housing 402 defines an opening 412 towhich the air intake line 30 is connected to place the air intake line30 in fluid communication with the hollow interior 404.

As shown in FIG. 15, the air plenum housing 402 encloses an air intakevalve 414 situated in bottom opening 416 of the air plenum housing 402.The air intake valve 414 extends through a corresponding opening 418 inthe compressor housing or crankcase 170. The air intake valve 414 may bea check valve or a reed-type valve adapted to allow cool air to be drawninto the crankcase 170 in response to the pistons 40, 140 moving towardtop dead center. As the pistons 40, 140 move to top dead center, avacuum develops in the crankcase 170 causing check valve plunger 420 (oran alternative reed) to open allowing air into the crankcase 170 fromthe air plenum housing 402. The air intake valve 414 prevents returnflow into the air plenum 402.

As further shown in FIGS. 15-16, one or more air discharge valves 422are provided in plate element 424 disposed in an opening in the bottomof the crankcase 170. The discharge valves may be check valves orreed-type valves as shown and allow the heated crankcase air to bevented to atmosphere. As the pistons 40, 140 move to bottom dead center,the air intake valve 414 is closed and the pressure in the crankcase 170increases. The increased pressure causes the air discharge valves 422 toopen venting the crankcase 170.

The two-valve method described above of bringing in cool air anddischarging hot air takes advantage of the large air volumes displacedas the pistons 40, 140 stroke up and down in their respective cylinders12, 112. Since both pistons 40, 140 travel from bottom dead center totop dead center at the same time, a significant volume of air isdisplaced. This displaced air is constantly going from pressure tovacuum as the crankshaft assembly 240 spins. By placing the air intakevalve 414 in the air plenum housing 402, ideally connected to an airfiltration element connected to the air inlet 408, filtered air is drawninto the crankcase 170. By placing the air discharge valves 422, on theopposite side of the crankcase 170 from the air intake valve 414, asshown in FIGS. 15-16, the cooling air will have to pass over thecrankshaft assembly 240 to reach the air discharge valves 422. As theair travels through the crankcase 170 it will remove heat from allradiating surfaces and the effects of gas blow-by and expel it from thecrankcase 170. Additional air intake valves 414 and air discharge valves422 may be added if needed to maximize the cooling air flows.

While embodiments of an oil-free air compressor for a rail vehicle areprovided in the foregoing description, those skilled in the art may makemodifications and alterations to these embodiments without departingfrom the scope and spirit of the invention. Accordingly, the foregoingdescription is intended to be illustrative rather than restrictive. Theinvention described hereinabove is defined by the appended claims andall changes to the invention that fall within the meaning and the rangeof equivalency of the claims are to be embraced within their scope.

The invention claimed is:
 1. An oil-free compressor for a rail vehicle,comprising: a compressor housing comprising at least a first housingportion and a second housing portion to define a compressor housinginterior; a first piston cylinder supported in a first opening in thecompressor housing; a second piston cylinder supported in a secondopening in the compressor housing and fluidly connected to the firstpiston cylinder; a multi-piece crankshaft assembly supported by thecompressor housing and linked to the pistons of the first and secondpiston cylinders by respective connecting rods; and an air plenum influid communication with the compressor housing interior to provide avolume of air to the compressor housing interior.
 2. An oil-freecompressor as claimed in claim 1, wherein the first housing portion andthe second housing portion form respective halves of the compressorhousing and are secured together with mechanical fasteners.
 3. Anoil-free compressor as claimed in claim 1, wherein the first pistoncylinder is larger than the second piston cylinder.
 4. An oil-freecompressor as claimed in claim 1, wherein the crankshaft assemblycomprises a crankshaft center section and two end sections.
 5. Anoil-free compressor as claimed in claim 4, wherein the end sectionscontain counterweights.
 6. An oil-free compressor as claimed in claim 4,wherein opposing ends of the crankshaft center section are securedwithin respective cavities in the end sections.
 7. An oil-freecompressor as claimed in claim 1, wherein the air plenum is in fluidcommunication with the first piston cylinder.
 8. An oil-free compressoras claimed in claim 1, further comprising an air intake valve in thecompressor housing enabling air to be drawn into the compressor housinginterior from the air plenum.
 9. An oil-free compressor as claimed inclaim 8, further comprising an air discharge valve in the compressorhousing enabling air to be discharged from the compressor housinginterior.
 10. An oil-free compressor for a rail vehicle, comprising: amulti-piece compressor housing; a first piston cylinder supported in afirst opening in the compressor housing; a second piston cylindersupported in a second opening in the compressor housing and fluidlyconnected to the first piston cylinder; a multi-piece crankshaftassembly supported by the compressor housing and linked to pistons ofthe first and second piston cylinders by respective connecting rods,wherein the connecting rods connect to a wrist pin associated with eachof the pistons, and the wrist pins are respectively supported by a drylubricant bushing to the associated piston; and an air plenum in fluidcommunication with the compressor housing interior to provide a volumeof air to the compressor housing interior.
 11. An oil-free compressor asclaimed in claim 10, wherein the compressor housing comprises at least afirst housing portion and a second housing portion.
 12. An oil-freecompressor as claimed in claim 11, wherein the first housing portion andthe second housing portion form respective halves of the compressorhousing and are secured together with mechanical fasteners.
 13. Anoil-free compressor as claimed in claim 10, wherein the first pistoncylinder is larger than the second piston cylinder.
 14. An oil-freecompressor as claimed in claim 10, wherein the crankshaft assemblycomprises a crankshaft center section and two end sections.
 15. Anoil-free compressor as claimed in claim 14, wherein the end sectionscontain counterweights.
 16. An oil-free compressor as claimed in claim14, wherein opposing ends of the crankshaft center section are securedwithin respective cavities in the end sections.
 17. An oil-freecompressor as claimed in claim 10, wherein the air plenum is in fluidcommunication with the first piston cylinder.
 18. An oil-free compressoras claimed in claim 10, further comprising an air intake valve in thecompressor housing enabling air to be drawn into the compressor housinginterior from the air plenum.
 19. An oil-free compressor as claimed inclaim 18, further comprising an air discharge valve in the compressorhousing enabling air to be discharged from the compressor housinginterior.
 20. An oil-free compressor as claimed in claim 10, wherein thedry lubricant bushing comprises a PEAK liner.